1. Technical Field
A method and apparatus for tipping, cutting and sorting surgical sutures is disclosed. More particularly, the present disclosure describes a method and apparatus for automating the steps of tipping, cutting and sorting surgical sutures.
2. Background of the Art
For many years, surgeons have employed needle-suture combinations in which a suture of ligature is attached to the shank end of a needle. Such needle-suture combinations are provided for a wide variety of monofilaments and braided suture materials, both absorbable and non-absorbable, e.g, catgut, silk, nylon, polyester, polypropylene, linen, cotton, and absorbable synthetic materials such as polymers and copolymers of glycolic and lactic acid.
Needle-suture combination fall into two general classes: standard, or non-detachable, needle attachment and removable, or detachable, needle attachment. In the case of standard needle attachment, the suture is securely attached to the needle and is not intended to be separable therefrom, except by cutting or severing the suture. Removable needle attachment, by contrast, is such that the needle is separable from the suture in response to a force exerted by the surgeon. Minimum acceptable forces required to separate a needle from a suture (for various suture sizes) are set forth in the U.S. Pharmacopoeia ("USP"). As to detachable needles, the USP prescribes individual pull-out forces and average pull-out forces as measured for five needle-suture combinations. The pull-out forces for both standard and removable needle-suture attachment set forth in the USP are hereby incorporate by reference.
One typical method for securing a suture to a needle involves providing a cylindrical recess in the shank end of a needle and securing a suture therein. For examples, U.S. Pat. No. 1,558,037 teaches the addition of a cement material to a substantially cylindrical recess to secure the suture therein. Additional methods for bonding a suture within a needle bore are described in U.S. Pat. Nos. 2,928,395 (adhesives) and 3,394,704 (bonding agents). Alternatively, a suture may be secured within an axial bore in a needle by swaging the needle in the region of the recess. See, e.g., U.S. Pat. No. 1,250,114. Additional prior art methods for securing a suture within a needle bore include expansion of a catgut suture through the application of heat (U.S. Pat. No. 1,665,216), inclusion of protruding teeth within the axial bore to grasp an inserted suture (U.S. Pat. No. 1,678,361) and knotting the end of the suture to be inserted within the bore to secure the suture therein (U.S. Pat. No. 1,757,129).
Insertion of sutures into a hole, recess or tube for attachment to surgical needles presents problems peculiar to suture needle combinations. Braided multifilament sutures in particular are difficult to insert into the very small aperture of a surgical needle: unless modified, they are too limp for the suture tip to be controlled for insertion and they have a tendency to "broom ", i.e., the filaments have a tendency to flare out at the cut end so that the diameter of the cut end exceeds the diameter of the needle hole. Various techniques have been employed to modify sutures to overcome the problems of limpness and brooming. One known method employs a tipping agent, which is a material used to coat the suture to stiffen the filaments and adhere them together.
Typically, a suture to be tipped is first placed under tension to reduce slack so that the suture may be maintained in a predetermined position on a frame or rack or other suture holding device. Optionally, the tension may be such as to reduce the diameter of the suture. See, Canadian Pat. No. 1,009,532. The suture is then dipped into the tipping solution and allowed to dry while under tension. The sutures are dried, for example, by being warmed in a drying oven at about 225.degree. F. for about 10 minutes. After drying the sutures can be cut and released from tension. The process results in a tipped end on each side of a cut, with the tipping agent adhering the suture filaments to one another to prevent brooming, thereby facilitating insertion of the suture end into a needle bore. Where tension has optionally been employed to reduce the suture diameter, release of the tension will allow the suture to expand to its original diameter except at the tipped portion. This can further facilitate insertion of the end into a needle.
Tipping agents may be dissolved in solvents to form dipping solutions. By way of example, Mariotte mixture is a dipping solution comprising nylon dissolved in isopropyl alcohol. Other polymers and solvents may also be used. Gould mixture is a dipping solution comprising nylon dissolved in methanol. At least one major manufacturer of surgical needles recommends use of Mariotte mixture or Gould mixture for tipping sutures. A multitude of other tipping agents, including polymers and solvents, have been proposed. For example McGregor (U.S. Pat. No. 3,890,975) discloses coating the suture with a binding resin or adhesive. The composition may be any non-toxic adhesive composition, either organic, inorganic or a hybrid. Suitable organic materials are such natural products as starch, dextrin, asphalt, animal and vegetable proteins, natural rubber, shellac; semi-synthetic products such as cellulose nitrate and the other cellulosics, polyamides derived from dimer acids, or castor-oil based polyurethanes; and well-known synthetic resins such as vinyl-type addition polymers, both resins and elastomers, polyvinyl acetate, polyvinyl alcohol, acrylics, unsaturated polyesters, butadiene/acrylonitrile, butadiene/styrene, neoprene, butyl robber, polyisobutylene, and polymers formed by condensation and other stepwise mechanisms, i.e., epoxies, polyurethanes, polysulfide rubbers, and the reaction products of formaldehyde with phenol, resorcinol, urea, and melamine. McGregor states that particularly preferred bonding compositions are epoxide resins and polyester resins.
Schmitt U.S. Pat. No. 3,736, 646 discloses that it is known to tip braided sutures by dipping the end of the suture in plastic such as a polymer solution in isopropyl alcohol. Schmitt suggests that for absorbable sutures an absorbable tipping agent is desirable, and proposes that a copolymer of lactic and glycolic acid dissolved in a suitable organic solvent, such as xylene or toluene, be applied to tip the suture.
Nichols U.S. Pat. No. 2,734,506 discloses a dipping solution of polymers of methacrylic acid esters in an organic solvent such as toluene, xylene acetone, ethyl acetate, methylethyl ketone, or naphtha.
Shepherd et al. U.S. Pat. No. 3,849, 185 discloses the use of an acrylic casting syrup as a tipping agent, the syrup being fully polymerized after being applied to the suture.
In addition, paraffin/hexane solution (10% paraffin) has been used as a suture coating agent as well as Arrochem (TM), a nylon resin plus methanol composition manufactured by Arrochem, Inc. of 201 Westland Farm Road, Mt. Holly, N.C. 28120, and SILASTIC (TM) Medical Adhesive (a silicon elastomer composition manufactured by Dow Coming Co.).
U.S. Pat. No. 5,269,808 to Proto et al., discloses a method and apparatus for tipping sutures which may be employed for both coated and uncoated sutures. The method described in U.S. Pat. No. 5,269,808 includes winding the suture around a drum while continuously monitoring the suture diameter in x and y directions and adjusting the tension on the suture to control the suture diameter as it is being wound. The drum is then placed in an apparatus which passes selected portions of the suture through a mist of cyanoacrylate tipping agent generated by ultrasonic atomization. The tipping agent quickly cures and the tipped portion of the suture may be cut to create a tipped end for insertion into a surgical needle to form a needle suture device.
Another method which has been employed for treating sutures involves melt fusion, as described in U.S. Pat. No. 4,832,025, issued to Coates. The suture is heated to a temperature at least high enough to "melt fuse" a portion of the outer filaments of the suture. According to Coates, such temperature is typically about 260.degree. C. to 300.degree.0 C. (500.degree. F. to 572.degree. F.). Exposure of synthetic sutures to such extreme temperatures melt fuses the filaments, and the melt fused suture portion stiffens upon cooling. Melting of the filaments has the effect of holding the filaments together when the suture is cut. It also causes stiffening of the suture which facilitates insertion of the suture end into the drilled hole of a needle. However, the melt fusion of suture has significant drawbacks.
Firstly, the melt fusion of filaments weakens the suture, whose tensile Strength is degraded in proportion to the extent of melt fusion.
Secondly, melt fusion causes an irreversible change in the filaments which result in permanent stiffening and permanent loss of tensile strength.
Thirdly, with the extreme temperatures disclosed by Coates for melt fusion an inconveniently short heating cycle is required. For example, for a size 3/0 silicone coated polyester suture heated to between 260.degree. C. to 300.degree. C. in a 4 mm. diameter heating tunnel, the heating time is no more than about 3 seconds. Such short heating time makes it difficult to control the process and leads to inconsistencies and variations in the melt fused tipping process.
U.S. Pat. No. 5,156,788 to Chesterfield et al., discloses a method and apparatus for tipping sutures by delimiting a portion of the suture and heating the delimited portion under predetermined time and temperature conditions to reversibly stiffen the delimited portion upon cooling. The cooled, stiffened suture portion is cut to provide a suitably stiffened, non-brooming suture tip for insertion into a needle.
Although tipped sutures prepared in accordance with the above procedures may have been used successfully, there are several drawbacks with the use of tipping solutions and melt fusing or heat tipping. The main problems relate to tipping consistency and process control. Nonuniform solvent evaporation, which may be caused by variations in the solvent, oven temperature and heating time can result in inconsistent tipping. Furthermore, the dried residue of polymer left after evaporation can flake off or develop cracks.
A further consideration pertinent to suture tipping is that sutures are often prepared with lubricant coatings such as absorbable polymers, silicone or fatty acid salts in order to increase lubricity and to improve "tie-down" performance, i.e., the ease of sliding a knot down the suture into place. Such lubricant coatings typically are incompatible with the materials and methods currently employed for tipping sutures. In particular, prior known tipping agents do not adhere well to lubricant coated sutures, which may result in inconsistent tipping or an undesirable reduction of suture-needle pull out force. The melt fusing method of tipping may destroy the lubricant coating or render it less effective in areas away from the needle.
A further consideration in attachment of sutures to needles is matching the diameter of the suture tip to the needle hole size. For some types of needle-suture attachment, e.g., swaged removable needle-suture attachment, it may be necessary to sort sutures based on a narrow range of diameter for attachment to certain needles. Typically, such sorting has been a manual task requiring an operator to measure the diameter of each cut, tipped suture and sort the sutures according to the desired needle-suture attachment to be accomplished.
It would be desirable to provide an automated apparatus and method for tipping, cutting and, if necessary, sorting sutures.